Pore Size Distribution Analysis of Coal-Based Activated Carbons: Investigating the Effects of Activating Agent and Chemical Ratio (original) (raw)
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Preparation and characterization of activated carbon from a low rank coal
Carbon, 1996
Powdered activated carbon has been prepared from lignitic coal of Lakhra (Pakistan) by a chemical activation method using ZnCl, as an activating agent. Different process variables have been established after a series of experiments and an impregnation ratio of 1: 2, an activation temperature of 650°C and a duration of 1 hour have been found to be appropriate for its preparation. It has been found that the char is obtained in high yield with iodine and methylene blue numbers of 990 and 205, respectively. Different parameters based on adsorption of benzene at 293 K under reduced pressure have been calculated using DR equation with micropore volume W,=O.46 cm3/g, an average pore width L= 0.98 nm and a microporous surface area S,, = 942 m2/g. The nonporous surface area S, calculated by the t/F method is 142 m'/g. FTIR spectra of this sample show the presence of acidic functional carboxylic groups developed on its surface after activation. Their predominance is further confirmed by neutralization with different alkalis.
International Journal of Chemical Reactor Engineering, 2017
Activated carbons of various features were produced by the impregnation of local coal samples that were taken from Kilimli region of Zonguldak (Turkey) with chemical agents KOH, NaOH and ZnCl2 at different temperatures (600–800 °C) and concentrations (1:1–6:1 agent:coal), for their evaluation in CO2 adsorption studies. BET, DR, t-plot and DFT methods were used for the characterization of carbon samples based on N2 adsorption data obtained at 77 K. The pore sizes of activated carbons produced were generally observed to be in between 13–25 Å, containing highly micropores. Mesopore formations were higher in samples treated with ZnCl2. The highest value for the BET surface area was found as 2,599 m2 g−1 for the samples treated with KOH at 800 °C with a KOH to coal ratio of 4:1. It was observed that the CO2 adsorption capacities obtained at atmospheric pressure and 273 K were considerably affected by the micropore volume and surface area. The highest CO2 adsorption capacities were found ...
Adsorption isotherms and kinetics of activated carbons produced from coals of different ranks
Water Science and Technology, 2015
Activated carbons (ACs) from six coals, ranging from low-rank lignite brown coal to high-rank stone coal, were utilized as adsorbents to remove basic methylene blue (MB) from an aqueous solution. The surface properties of the obtained ACs were characterized via thermal analysis, N2 isothermal sorption, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Boehm titration. As coal rank decreased, an increase in the heterogeneity of the pore structures and abundance of oxygen-containing functional groups increased MB coverage on its surface. The equilibrium data fitted well with the Langmuir model, and adsorption capacity of MB ranged from 51.8 to 344.8 mg g−1. Good correlation coefficients were obtained using the intra-particle diffusion model, indicating that the adsorption of MB onto ACs is diffusion controlled. The values of the effective diffusion coefficient ranged from 0.61 × 10−10 to 7.1 × 10−10 m2 s−1, indicating that ACs f...
Adsorption
In this paper we study a method for the determination of the micropore volume distribution function of activated carbons. This method is based on the Integral Adsorption Equation concept (IAE). The micropore volume distribution function is assumed to be a Gaussian of which the parameters are unknown. These parameters are determined using adsorption isotherms of carbon dioxide on a given activated carbon (F30/470 CHEMVIRON CARBON) at 278, 288, 298, 303, 308, 318 and 328 K and for pressures up to 100 kPa. Several local adsorption models are used (Langmuir, Volmer, Fowler-Guggenheim, Hill-de Boer). The influence of the choice of the local model on the pore volume distribution function is discussed. The physical validity of this function and the performances of the different models are presented. It appears that the effect of the temperature on the adsorption isotherms is difficult to model over a wide range of relative pressure. The Hill-de Boer and the Langmuir local models are the most efficient (average errors respectively equal to 3.53% and 2.80% in the studied range of temperature and pressure). They provide the most meaningful parameters for the pore volume distribution function.
Materials
In this study, the preparation of activated carbons from various materials of biomass origin by activation with potassium hydroxide and a comprehensive computer analysis of their porous structure and adsorption properties based on benzene (C6H6) adsorption isotherms were carried out. In particular, the influence of the mass ratio of the activator’s dry mass to the char mass on the formation of the microporous structure of the obtained activated carbons was analysed. The summary of the analyses carried out based on benzene adsorption isotherms begged the conclusion that activated carbon with a maximum adsorption volume in the first adsorbed layer and homogeneous surface can be obtained from ebony wood at a mass ratio of the activator to the char of R = 3. The obtained results confirmed the superiority of the new numerical-clustering-based adsorption analysis (LBET) method over simple methods of porous structure analysis, such as the Brunauer–Emmett–Teller (BET) and Dubinin–Raduskevic...
Preparation and characterization of activated carbons from different kinds of coal
Proceedings of the Mongolian Academy of Sciences, 2020
Initial coal was purified in heavy liquid with a density 1.3 cm3 of ZnCl2 solution and purified coal was carbonized and the initial coal samples of each deposits were purified by pyrolysis. Thus, the yield of pyrolysis hard residue in the enriched sample was slightly higher than in the hard residue of initial coal. Therefore, pyrolysis hard residue of purified coal (carbonized sample) was activated at 800°C for 2 hours by preheated water steam. Activated carbons (ACs) and non-activated and non-carbonized coal from Baganuur, Ereen and Nariin Sukhait deposits were technically analyzed and their iodine number, BET surface area, pore volume and adsorption of methylene blue (MB) were determined. When these results were compared, these indicators increased 5-17 times in the Baganuur activated carbon (BN-AC), Ereen activated carbon (E-AC) and Nariin Sukhait activated carbon (NS-AC) as compared to inactivated coal.
Materials
The results of a study of the impact of activation temperature and the mass ratio of the activator to the carbonised precursor on the porous structure of nitrogen-doped activated carbons obtained from lotus leaves by carbonisation and chemical activation with sodium amide (NaNH2) are presented. The analyses were carried out via the new numerical clustering-based adsorption analysis, the Brunauer–Emmett–Teller, the Dubinin–Raduskevich, and the density functional theory methods applied to carbon dioxide adsorption isotherms. Carbon dioxide adsorption isotherms’ analysis provided much more detailed and reliable information about the pore structure analysed. The analyses showed that the surface area of the analysed activated carbons is strongly heterogeneous, but the analysed activated carbons are characterised by a bimodal pore structure, i.e., peaks are clearly visible, first in the range of pore size from about 0.6 to 2.0 nm and second in the range from about 2.0 to 4.0 nm. This pore...
In this work, the effect of activating agents on activated carbon produced from sub-bitumous coal was investigated. Chemical method of activation was employed. The coal sample was subjected to pretreatment and later activation and carbonization. The pretreated coal was impregnated with activating agent at ratios of combination ranging from 1/1 to 1/4 and then heated to a given temperature at specific time intervals. The resulting product was carbonized in a furnace at a temperature of 6000 -10000C for 2 hours. The characterization tests conducted on the activated carbon products showed that the adsorptive properties vary with the nature of activating agent, impregnation ratio of activating agent and temperature of activation. The assessed parameters of surface area, iodine number, porosity, fixed carbon etc recorded substantial increment for the most of the activating agents. The KOH activating agent produced the best performance in all the conditions investigated. FTIR analysis indicates significant variations in the functional groups while SEM-morphology study of the surface of the activated carbon produced shows remarkable pore volume development.
International Journal of Chemical Reactor Engineering, 2018
Activated carbons were produced from coal by activations applying physical and chemical (with KOH) treatments for adsorption of selected organic vapors. Physical activations were carried out at 400-900°C under N 2 /CO 2 flow. The effects of different variables such as carbonization temperature and flow rate on the final porous texture were investigated. Chemical activation gave more effective results in terms of both porosity development and adsorption capacity. Pore characterization of carbon samples was evaluated with the observation of N 2 adsorption-desorption isotherms at 77 K. The adsorption of isopropyl alcohol, acetone and ethyl alcohol on the coal derived activated carbons were determined by a volumetric technique at room temperature. The highest surface area was obtained as 1904 m 2 /g by KOH treatment at 800°C. The adsorption isotherm data of the selected organic vapors on carbon samples were compared with the BET, Langmuir, Freundlich, Dubinin-Radushkevich, Dubinin-Astakhov, Harkins-Jura, Henderson, Halsey and Smith adsorption models. Adsorption capacities of organic vapors for carbon samples were related with the development of surface area. Among the four chemically activated carbons produced K1_K_600, K1_K_700 and K1_K_800 showed better isopropyl alcohol and acetone adsorption than the commercial activated carbon. K1_K_700 and K1_K_800 samples showed better ethyl alcohol adsorption. Isopropyl alcohol, acetone and ethyl alcohol adsorption capacities of the obtained sample that had the maximum surface area were determined as 39.7, 44 and 43.5 %, respectively. Results indicate that activated carbons prepared with KOH at 600-800°C could be effectively used for the adsorption of organic vapors.
Some remarks on the calculation of the pore size distribution function of activated carbons
Journal of Colloid and Interface Science, 2006
Different authors investigated the effects of geometric and energetic heterogeneities on adsorption and on carbon characterization methods. In most theoretical studies carbon structure is modeled as parallel infinite graphite walls that form ideal slit-shaped pores of the fixed widths. In the literature there is the lack of systematic studies showing the influence of pore structural and Lennard-Jones (LJ) potential parameters on the poresize distribution functions. Moreover, the parameters characterizing the properties of the adsorbed phase and the heterogeneity of the adsorbent surface should be taken into account. The Nguyen and Do method with proposed by us ASA algorithm, were utilized for the assessment of the porosity from the series of almost few thousands numerically generated local adsorption isotherms. The values of the mentioned-above parameters are varied over the wide range (ca. ±20%) of the reference ones. Different types of the theoretical and experimental adsorption isotherms (nitrogen at 77 K) were taken into account as the global ones. They were related to the mechanism of the primary, secondary or mixed micropore filling. The variations in some above-mentioned parameters have significant effects only for PSDs (and for average pore widths) corresponding to the primary micropore filling mechanism. On the other hand, for the process of the secondary micropore filling, the influence of these parameters (without the BET coefficient for adsorption on a "flat" surface, c s,B ) is rather insignificant. Nevertheless the differences between local and global adsorption isotherms (in the whole range of relative pressures) the absence of micropores having pore half width equal to ca. 1 nm on PSDs was observed for studied adsorbate-adsorbent systems with exceptions of the strictly microporous adsorbents and/or the low values of c s,B . Comparison of the experimental data with the generated theoretical isosteric enthalpy of adsorption indicates that the phenomenal uptake observed from experiment can be explained in terms of the reasonable solid-fluid interaction parameters. Therefore, we varied the heterogeneity of the adsorbent surface via the strength and the range of the solid-fluid potential and the parameter c s,B in order to reproduce the experimental data of enthalpy of adsorption. Note that similar procedure was applied by Wang and Johnson to reproduce some hydrogen adsorption data measured for carbon nanofibres. The analysis of the obtained results shows that the selection of the values of the parameters of the intermolecular interactions and the quantities characterizing the properties of the adsorbed phase and the heterogeneity of the adsorbent walls for molecular simulations should be made with care and the influence of possible errors should be considered.